The Digestive System

Overview of the Digestive System

23 PART 1 • Organs are divided into two groups The Digestive System • Alimentary canal • Mouth, pharynx, and esophagus • Stomach, small intestine, and large intestine • Accessory digestive organs • Teeth and tongue • Gallbladder, salivary glands, liver, and pancreas • Accessory organs are connected to the alimentary canal by ducts PowerPoint® Lecture Presentations prepared by Leslie Hendon • Secretions contribute to breakdown of foodstuffs University of Alabama, Birmingham © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc.

Figure 23.1 The alimentary canal and the accessory digestive organs. Abdominal Regions

Mouth (oral cavity)

Parotid gland Sublingual gland • Four lines divide abdominal wall into nine Tongue Salivary glands Submandibular gland regions • Midclavicular lines—vertical lines of grid Pharynx Esophagus

Stomach • Subcostal plane—superior horizontal line Pancreas (Spleen) • Connects inferior points of costal margin Liver

Gallbladder Transverse • Transtubercular plane—inferior horizontal line colon Descending Duodenum colon • Connects tubercles of iliac crests Small Jejunum Ascending intestine Ileum colon Large intestine Cecum Sigmoid colon Rectum Appendix Anus Anal canal © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc.

Figure 23.2a Divisions of the anterior abdominal wall. Figure 23.2b Divisions of the anterior abdominal wall.

Liver Diaphragm Right Left Epigastric hypochondriac hypochondriac region region region Gallbladder Stomach

Transverse colon Right Left Ascending colon Umbilical of large intestine lumbar lumbar of large intestine region region region Small intestine Descending colon of large intestine Cecum Right iliac Hypogastric Left iliac Initial part of (pubic) (inguinal) (inguinal) Appendix sigmoid colon region region region Urinary bladder

1 Figure 23.3 Peritoneum and the Digestive System Organs (1 of 2) Abdominal Quadrants

• A simpler method of sectioning the anterior abdominal wall • Right upper quadrant • Left upper quadrant • Right lower quadrant • Left lower quadrant

Figure 23.3 Peritoneum and the Digestive System Organs (2 of 2) The Peritoneal Cavity and Peritoneum

• Peritoneum—a serous membrane • Visceral peritoneum—surrounds digestive organs • Parietal peritoneum—lines the body wall • Peritoneal cavity—a slitlike potential space

The Peritoneal Cavity and Peritoneum The Peritoneal Cavity and Peritoneum

• Mesentery—a double layer of peritoneum • Ventral mesenteries • Holds organs in place • Falciform ligament • Sites of fat storage • Binds anterior part of liver to anterior abdominal wall • Provides a route for circulatory vessels and nerves • Lesser omentum • Attaches liver to the lesser curvature of stomach

2 Figure 23.4a The mesenteries. The Peritoneal Cavity and Peritoneum Falciform ligament Liver • Dorsal mesenteries Gallbladder

• Greater omentum Spleen Stomach • Connects greater curvature of stomach to posterior abdominal wall Ligamentum teres • A “fatty apron” Greater omentum • Transverse mesocolon Small intestine • Holds transverse colon in place • Sigmoid mesocolon Cecum • Connects the sigmoid colon to posterior pelvic wall

Figure 23.4b The mesenteries. Figure 23.4c The mesenteries.

Greater omentum Liver

Gallbladder Transverse colon Lesser omentum Transverse mesocolon Stomach Duodenum

Transverse colon Descending colon Mesentery Small intestine

Sigmoid mesocolon Jejunum Cecum Sigmoid colon Urinary bladder Ileum

Figure 23.4d The mesenteries. The Peritoneal Cavity and Peritoneum Ligamentum teres Gallbladder Lesser omentum Spleen • Retroperitoneal organs Liver Gastrosplenic ligament Behind the peritoneum Transverse Pancreas • mesocolon Stomach, pyloric part Duodenum, • Peritoneal organs superior part Transverse colon Duodenum, Duodenojejunal flexure horizontal part • Digestive organs that keep their mesentery Greater omentum

Descending colon Ascending colon Mesentery (cut) Sigmoid mesocolon

Rectum Ileum Cecum

3 Table 23.1 Summary of Intraperitoneal and Secondarily Retroperitoneal Digestive Organs in the Abdomen and Pelvis Secondarily Retroperitoneal Organs

• Initially formed within peritoneum • Become retroperitoneal • Fuse to posterior abdominal wall

Digestive Processes Digestive Processes

• Ingestion—occurs in the mouth • Chemical digestion—complex molecules broken down to chemical components • Propulsion—movement of food • Mouth • Peristalsis—major means of propulsion • Stomach • Mechanical breakdown—prepares food for chemical digestion • Small intestine • Chewing, churning food in stomach, • Absorption—transport of digested nutrients segmentation • Defecation—elimination of indigestible • Segmentation is rhythmic local constrictions of substances as feces intestine

Figure 23.5 Activities of the gastrointestinal tract. Peristalsis Ingestion Food

Mechanical breakdown Pharynx Major means of propulsion • Chewing (mouth) Esophagus • • Churning (stomach) • Segmentation Propulsion (small intestine) • Swallowing (oropharynx) • Adjacent segments of the alimentary canal • Peristalsis (esophagus, Digestion stomach, small intestine, relax and contract large intestine)

Stomach

Absorption

Lymph vessel

Small intestine Blood Large vessel intestine

Mainly H2O Feces

Anus Defecation

4 Figure 23.6a Peristalsis and segmentation. From mouth Segmentation

• Rhythmic local contractions of the intestine • Mixes food with digestive juices

Figure 23.6b Peristalsis and segmentation. Histology of the Alimentary Canal Wall

• Same four layers from esophagus to anus • The mucosa—innermost layer • Consists of • Epithelium • Lamina propria • Muscularis mucosae Segmentation: Nonadjacent segments of alimentary tract • The submucosa—external to the mucosa organs alternately contract and relax, moving the food forward • Contains blood and lymphatic vessels, nerve then backward. Food is mixed and slowly propelled. fibers

Figure 23.7a Histological layers of the alimentary canal. Histology of the Alimentary Canal Wall

Intrinsic nerve plexuses Myenteric nerve plexus • The muscularis externa—external to the Submucosal nerve plexus submucosa Glands in submucosa

• Two layers Mucosa Epithelium Lamina propria • Circular muscularis—inner layer Muscularis mucosae

• Longitudinal muscularis—outer layer Submucosa

Muscularis externa • The serosa—the outermost layer Circular layer Longitudinal layer • Is the visceral peritoneum Serosa Epithelium Connective tissue Nerve Lumen Artery Gland in mucosa Vein Duct of gland outside Mucosa associated Mesentery Lymphatic vessel alimentary canal lymphoid tissue Longitudinal and cross-sectional views through the small intestine

5 Figure 23.7b Histological layers of the alimentary canal. Smooth Muscle

• Primarily found in walls of viscera Mucosa • Fibers elongated • Have one centrally located nucleus Submucosa • Grouped into sheets Muscularis externa • Longitudinal layer—parallel to long axis of Serosa organ • Circular layer—deeper layer, fibers run around circumference of organ Light micrograph cross section through the small intestine (85×)

Figure 23.8 Arrangement of smooth muscle in the walls of hollow organs. Smooth Muscle Contraction

• Mechanism of contraction • Myofilaments operate by interaction with cytoskeleton Longitudinal layer of smooth muscle (shows smooth muscle fibers in cross section, 215×) • Dense bodies—correspond to Z-discs of skeletal muscle

Small intestine • Sliding myofilaments shorten the muscle cell by Mucosa pulling on cytoskeleton Location and plane of Cross section of the intestine Circular layer of smooth section shown in (b) showing the smooth muscle muscle (shows longitudinal layers (one circular and the views of smooth muscle 2+ other longitudinal) running at fibers, 215×) • Entry of Ca into sarcoplasm stimulates right angles to each other contraction

Figure 23.9 Cytoskeletal elements involved in the contraction of smooth muscle. Smooth Muscle Contraction Intermediate Caveolae Gap junctions filament • Contraction is slow and sustained • Takes 30x longer to contract and relax Nucleus Dense bodies • Resistant to fatigue Relaxed smooth muscle fiber (note that gap • Smooth muscle of arteries and visceral organs junctions connect adjacent fibers) must sustain contraction over long periods Nucleus • Energy requirements are low Dense bodies • Mitochondria are not abundant

Contracted smooth muscle fiber

6 Figure 23.10 Innervation of smooth muscle. Innervation of Smooth Muscle Varicosities • Innervated by ANS

• Few fibers per sheet innervated Autonomic Smooth nerve fibers muscle • Sheet of smooth muscle contracts as a unit innervate cell most smooth • Called single-unit innervation muscle fibers. • Multiunit innervation • Each smooth muscle cell innervated • Iris of eye and arrector pili muscles Synaptic Mitochondrion Varicosities release vesicles their neurotransmitters into a wide synaptic cleft (a diffuse junction).

Nerve Plexuses The Mouth and Associated Organs

• Myenteric nerve plexus • Mouth (oral cavity) • Lies between circular and longitudinal muscularis • Mucosa-lined cavity • Controls peristalsis and segmentation • Boundaries are • Submucosal nerve plexus • Lips anteriorly • Lies in submucosa • Cheeks laterally • Palate superiorly • Signals glands to secrete • Tongue inferiorly • Innervation • Fauces of oropharynx posteriorly • Sympathetic and parasympathetic motor fibers • Visceral sensory fibers

Figure 23.11a Anatomy of the mouth. The Mouth and Associated Organs Soft palate Palatoglossal arch Uvula

Hard palate • The mouth—oral cavity Oral cavity • Mucosal layer Palatine tonsil • Stratified squamous epithelium Tongue Oropharynx • Lamina propria Lingual tonsil • The lips and cheeks Epiglottis • Formed from orbicularis oris and buccinator Hyoid bone muscles, respectively Laryngopharynx Esophagus

Trachea

7 Figure 23.11b Anatomy of the mouth. Anatomy of the Mouth Gingivae Upper lip (gums) Superior labial Palatine frenulum • The labial frenulum raphe Palatoglossal • Connects lips to gum Hard palate arch Soft palate Palatopharyngeal arch • The palate Uvula Posterior wall Palatine of oropharynx • Forms the roof of the mouth tonsil Tongue Sublingual • Boundaries of the fauces fold with Lingual frenulum openings of Opening of • Palatoglossal arches sublingual ducts submandicular duct Oral vestibule • Palatopharyngeal arches Gingivae (gums) Lower lip Inferior labial frenulum Anterior view

The Tongue The Superior Surface of the Tongue

• Interlacing fascicles of skeletal muscle • Tongue papillae • Grips food and repositions it • Filiform papillae—no taste buds • Helps form some consonants • Fungiform papillae • Intrinsic muscles—within the tongue • Vallate papillae • Extrinsic muscles—external to the tongue • Sulcus terminalis • Lingual frenulum • Marks border between mouth and pharynx • Secures tongue to floor of mouth • Posterior one-third of tongue lies in oropharynx • Lined with lingual tonsil

Figure 23.12 The dorsal surface of the tongue. Epiglottis The Teeth Palatopharyngeal arch Palatine tonsil • Deciduous teeth—20 teeth Lingual tonsil • First appear at 6 months of age Palatoglossal arch • Permanent teeth—32 teeth Terminal sulcus • Most erupt by the end of adolescence Foliate papillae • Dental formula—shorthand Vallate papilla

Medial sulcus • Formula for adult dentition indicates number and of the tongue position of teeth Dorsum of tongue • 2I, 1C, 2P, 3M Fungiform papilla Filiform papilla © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc.

8 Figure 23.13a Human dentition. Figure 23.13b Human dentition. Incisors Central (6–8 mo) Lateral (8–10 mo)

Canine (eyetooth) (16–20 mo)

Molars First molar (10–15 mo) Deciduous (milk) teeth Second molar (about 2 yr)

Incisors Central (7 yr) Lateral (8 yr) Canine (eyetooth) (11 yr)

Premolars (bicuspids) First premolar (11 yr) Deciduous teeth Permanent teeth Second premolar (12–13 yr)

Molars First molar (6–7 yr) Second molar (12–13 yr) Third molar Permanent (wisdom tooth) teeth (17–25 yr)

Vessels and Nerves to the Teeth Tooth Structure

• Upper teeth • Crown—exposed surface • Innervation is superior alveolar nerves • Root—in tooth socket branching from maxillary division of CN V • Outer layer is enamel • Lower teeth • Dentin—underlies enamel • Innervation is inferior alveolar nerves branching from mandibular branch of CN V • Pulp cavity—center of tooth • Arterial supply to teeth • Superior and inferior alveolar arteries (branching from maxillary arteries)

Figure 23.14 Longitudinal section of a canine tooth within its bony tooth socket. Enamel The Salivary Glands Dentin Crown Dentinal tubules • Produce saliva Pulp cavity (contains blood vessels and nerves) • Compound tubuloalveolar glands Neck Gingival sulcus • Parotid glands Gingiva (gum) • Parotid duct—parallel to zygomatic arch Cement • Contain only serous cells Root canal Root • Submandibular glands Periodontal ligament • Lie along medial surface of mandible • Sublingual glands Apical • Lie in floor of oral cavity foramen

9 Figure 23.15 The major salivary glands. The Pharynx

• Oropharynx and laryngopharynx • Passages for air and food Tongue

Teeth Parotid gland • Lined with stratified squamous epithelium Ducts of sublingual Parotid duct gland Masseter muscle • External muscle layer Frenulum of tongue Body of mandible (cut) Sublingual • Consists of superior, middle, and inferior gland Posterior belly of digastric muscle Mylohyoid pharyngeal constrictors muscle (cut) Submandibular duct Anterior belly of digastric muscle Submandibular Mucous cells Serous cells gland forming demilunes

The Esophagus The Esophagus

• Gross anatomy—muscular tube • Microscopic anatomy • Begins as a continuation of the pharynx • Epithelium is stratified squamous epithelium • Joins the stomach inferior to the diaphragm • When empty, mucosa and submucosa are in • Cardiac sphincter—closes lumen to prevent longitudinal folds stomach acid from entering esophagus • Mucous glands—primarily compound tubuloalveolar glands

Figure 23.16 Microscopic structure of the esophagus. The Esophagus

• Muscularis externa • Skeletal muscle

• First one-third of length Mucosa (stratified squamous epithelium) Esophagus- stomach • Mixture of skeletal and smooth muscle Submucosa junction (areolar connective • Middle one-third of length tissue) Lumen Muscularis externa Simple columnar • Smooth muscle Circular layer epithelium of Longitudinal layer stomach • Inferior one-third of length Adventitia (fibrous connective tissue)

Cross section through Esophagus-stomach junction, • Adventitia esophagus (3×) longitudinal section (85×) • Most external layer of esophagus

10 Figure 23.17a Gross anatomy of the stomach. Cardia The Stomach Fundus

Esophagus • Site where food is churned into chyme Muscularis externa Serosa • Secretion of pepsin begins protein digestion Longitudinal layer Circular layer Body • Functions under acidic conditions Oblique layer Lesser Lumen • Food remains in stomach approximately 4 curvature Rugae of hours mucosa • Regions of the stomach

Figure 23.17b Gross anatomy of the stomach. Microscopic Anatomy of the Stomach

• Muscularis has three layers Liver Fundus (cut) Body • Circular and longitudinal layers and oblique layer Spleen • Epithelium is simple columnar epithelium Lesser curvature • Mucosa dotted with gastric pits • Gastric glands—deep to gastric pits Greater curvature

Figure 23.18 Microscopic anatomy of the stomach.

Gastric pits

Microscopic Anatomy of the Stomach Surface epithelium (mucous cells)

Gastric Surface pit • Gastric glands of fundus and body epithelium Mucous neck cells Parietal cell

Mucosa Gastric • Mucous neck cells gland Lamina propria Chief cell Muscularis mucosae • Secrete a special mucus Submucosa (contains submucosal Oblique plexus) Enteroendocrine cell Pepsinogen Pepsin layer HCl Enlarged view of Circular Muscularis gastric pi